This invention relates to semiconductor devices and more specifically relates to a novel insulated gate bipolar transistor (IGBT) which cannot latch on.
IGBTs are well known devices and generally consist of a four layer device with a MOSgate. Thus, the devices generally employ a P type emitter layer which has an N+ buffer layer thereon and an Nxe2x88x92 body regions atop the buffer. P type base diffusions are then formed in the Nxe2x88x92 body regions and N type emitter diffusions are formed in the P type base regions. The N type emitter regions are spaced from the boundaries of the P bases to define invertible channel regions. A MOSgate structure is then formed atop these channel regions.
Thus, the device is basically a four layer structure with the upper three layers and lower three layers defining respective bipolar transistors. As is well known, if the sum of the gains of these transistors exceeds unity, the device will latch on, that is, will remain conductive even after the gate turn on signal is removed.
It would be desirable to make an IGBT which cannot latch on. It would be further desirable to simplify the manufacture of such IGBTs by reducing the number of junctions which must be formed, and by reducing the thickness need for the Nxe2x88x92 body.
In accordance with the invention, the emitter region (sometimes called a source region) of a conventional IGBT is replaced by a trench gate and a Schottky injecting contact on the Nxe2x88x92 body to initiate device conduction. As a result of the novel structure, the fourth layer (the N+ emitter layer) of a conventional IGBT is removed and the device no longer has cascaded bipolar transistors and cannot latch on. Furthermore, the Nxe2x88x92 body region, which is usually epitaxially deposited, can be much thinner for a given voltage rating so that a less expensive starting wafer and fewer diffusion steps are needed for the manufacture of the device.